Cholera can now be prevented effectively for five years with an oral vaccine, a clinical trial in India has shown.

The oral vaccine Shanchol, manufactured by Shantha Biotechnics of Hyderabad, India, was 65 per cent more effective than a placebo at protecting study subjects from the disease over five years.

With its ability to spread rapidly, cholera can overwhelm public health services and require substantial resources to tackle. African countries alone spent US$156 million on the disease in 2007 alone, according to Berni Nor, a research advisor at the Swedish International Development Cooperation Agency (Sida), which part-funded the vaccine's development.

In 2010, the WHO issued guidance supporting the use of oral cholera vaccines in public health programs in conjunction with other preventative measures such as ensuring access to clean drinking water.

The following year, the organization prequalified Shanchol, allowing trials aimed at getting it licensed for sale to begin. Studies have since shown the vaccine to be effective for up to three years.

Yet the study authors write that its use may be hindered in practice by the "perceived short duration of protection that the vaccine confers" compared with recommended vaccines for other diseases.

One other oral cholera vaccine, called Dukoral, has been prequalified by the WHO, but it is used mainly by Western people travelling to cholera-endemic regions and has not been used by developing nations. Another oral vaccine, mORC-Vax, has also been developed, but this has yet to be prequalified by the WHO.

Long-term study

"Earlier studies on Shanchol showed that, at two years, protective efficacy was 67 per cent; at three years, protective efficacy was 66 per cent. Our study intended to assess the ability of the vaccine to protect against infection for a longer period," says Sekhar Chakrabarti, deputy director of the National Institute of Cholera and Enteric Diseases (NICED) in Kolkata, India, where the studies were conducted from.

The trial involved 66,900 people living in a Kolkata slum. "The participants were given two doses of the vaccine two weeks apart in the period July 2006 to September 2006," says Suman Kanungo, an epidemiologist at NICED and one of the paper's authors.

Over the next five years, those given the vaccine were 65 per cent less likely to have a cholera episode serious enough for them to seek treatment than those given a placebo.

Affordable and accessible vaccine

Shanchol costs US$1.85 a dose, compared with US$5 per dose for its competitor Dukoral, according to Berni Nor. It is also easier to administer than Dukoral, which is sensitive to stomach juices and so has to be taken along with a 'buffer' draught that prevents immediate metabolism of the drug.

At present, Shanchol must be used before infection to prevent the disease, but clinical trials are being carried out in Dhaka, Bangladesh, to check its effect on people who already have the disease.

Keya Chaudhuri, a chief scientist at the Indian Institute of Chemical Biology in Kolkata, says she is excited about the extended period of protection that Shanchol provides. But she adds that the vaccine has been primarily tested in places where cholera is endemic and so subjects may already have some immunity to the disease.

"What needs to be tested is how well this vaccine performs on subjects who are not from cholera endemic zones," she points out.